1. Field of the Invention
The present invention relates to splicing the two different sections of a tubular heater. More specifically, the present invention relates to a method and apparatus for splicing together one end of a cold pin section with the end of a section having a heatable coil without additional parts or special preparation of the heater section ends.
2. Prior Art
Typically, heaters are comprised of an inner metal resistive coil, referred to as a heating element, surrounded by an insulating filler that is, in turn, surrounded by an outer metal sheath. Such heaters are well known in the art. These heaters are constructed with a sheath made from a round metal tube. These are sometimes referred to as xe2x80x9ctubular heaters,xe2x80x9d even if the sheath is rolled or flattened after manufacture.
In many applications, it is necessary to provide a tubular heater that has at least one heatable (xe2x80x9cheatablexe2x80x9d) section and at least one unheated (xe2x80x9ccoldxe2x80x9d) section. The heatable section generally includes a heating element coil that is helically-wound of electrically resistive material, surrounded by an insulating filler material, such as magnesium oxide, which is then surrounded by an outer metal sheath. The cold section generally has a power pin (also known as a xe2x80x9ccold pinxe2x80x9d). The cold section is surrounded by an insulating filler material that is, in turn, surrounded by a metal sheath similar to the sheath used in the heatable section. During manufacturing, the cold pin is coupled with the heating element coil of the heatable section. Voltage is then applied to the cold pin, which conducts the current to the heating element coil to generate heat. In other applications it may be necessary to manufacture tubular heaters with varying watt density along the length of the heater. Many variations in heater assembly necessitate the custom manufacture and splicing of these kind of tubular heaters.
One innovative way of splicing the heatable and cold sections is disclosed in U.S. Pat. No. 5,864,941 (xe2x80x9cthe ""941 patentxe2x80x9d) issued to Baichoo et al. assigned to Watlow Electric Manufacturing Company, the specification of which is incorporated in its entirety by reference. The ""941 patent teaches a method of splicing one end of a heatable section to an end of a cold section by first exposing a substantial section of the heating element coil from the end of the sheath of the heatable section by: 1) manually cutting away a portion of the sheath and insulating filler, 2) inserting a cold pin with a tapered end into the exposed end of heating element coil, and then 3) physically joining the two ends together. Finally, an insulating filler is placed around the cold pin and the cold pin-heating element junction while the metal sleeve is placed around the insulating filler. Preferably, the ends of the respective heatable and cold sections are attached to the metal sleeve by a conventional welding procedure and then the entire assembly is swaged to a uniform diameter.
The ""941 patent represents a much improved method of splicing heatable and cold sections of a tubular heater together over prior methods. However, further improvements are desirable. For instance, the splicing operation of the prior art requires manually cutting back the heater section to expose the heating element coil, then manually welding the cold pin to the heating element coil, insulating the welded section, sliding a metal tube over the insulated terminal to the sheath of the heatable section, followed by swaging the tube to complete the joint. Furthermore, the method of the ""941 patent requires that numerous different parts and material be kept in stock, such as metal sleeves and insulating filler.
Therefore, there appears a need in the art for an automated method and apparatus for splicing the ends of two tubular heater sections together without additional parts or special preparation of the heatable and cold section ends.
The primary object of the present invention is to provide an apparatus for splicing together the respective ends of a cold section with a heatable section of a tubular heater without additional parts or special manual preparation of the section ends.
Another object of the present invention is to provide an automated apparatus and related method for splicing together respective ends of a cold section with a heatable section of a tubular heater.
Another further object of the present invention is to provide an apparatus for splicing one end of a cold section with a heatable section of a tubular heater by melting a portion of the cold pin and physically joining it to the end of the heatable section.
These and other objects of the present invention are realized in the preferred embodiment of the present invention, described by way of example and not by way of limitation, which provides for a method and apparatus of splicing respective ends of a cold section with a heatable section of a tubular heater.
In brief summary, the present invention overcomes and substantially alleviates the deficiencies in the prior art by providing an apparatus for splicing a heatable section of a tubular heater to a cold section thereof. The heatable section of the tubular heater generates heat energy for heat transfer systems and includes an outer sheath having an insulating filler that surrounds a center heating element coil which extends substantially the length of the outer sheath. When properly assembled, electrical current is passed through the heating element coil which causes it to generate heat. The cold section of the tubular heater provides the necessary electrical current to the heatable section and includes an outer sheath with an insulating filler that surrounds an electrically conductive cold pin which extends substantially the length of the outer sheath. A properly assembled tubular heater of the present invention joins the heatable and cold sections together in a splicing operation such that electrical current passes from the cold pin to the heating element coil for generating heat energy.
The apparatus for splicing the tubular heater according to the present invention comprises an enclosure defining a chamber. This chamber includes a platform extending from one side of the enclosure having a notched portion formed along its center and a roller assembly extending through apertures formed along the opposite side of the enclosure. The enclosure further defines first and second opposed openings in communication with the chamber. The first and second openings are respectively aligned with the notched portion and the roller assembly. The roller assembly and platform include placement and staging portions aligned with the first and second openings, respectively, which stage the heatable and cold sections thereon and facilitate the movement of these sections during the splicing operation. The enclosure further comprises at least one welding tip which extends into the chamber and is adapted to melt the exposed end of the cold pin and then circumferentially weld the abutting ends of heating element and cold pin together during the splicing operation.
In accordance with the method of the present invention, a user first places the heatable section on the notched portion of the platform and the cold section on the placement portion of the roller assembly. The heatable and cold sections are then directed into the chamber through respective first and second openings to a predetermined depth therein. After entering the chamber, the exposed end of the heatable section contacts a stop located inside the enclosure and the welding tip is placed in close proximity with the end of the cold section having the cold pin exposed. The welding tip which initiates an electrical arc by imposing a high voltage between the welding tip and the cold pin turns the exposed portion of the cold pin into a molten pool. The welding tip is then directed out of contact with the cold pin and the ends of the heatable and cold sections are brought into physical contact with one another such that the molten pool of the cold pin and the exposed end of the heating element coil form a secure welded connection as the molten pool solidifies around the coil. A second welding tip is then brought into close proximity with the ends of the outer sheaths to form a circumferential weld joint along the juncture of the ends as the heatable and cold sections are rotated about their centers by the staging portion of the roller assembly, thereby establishing a splice therebetween.
Additional objects, advantages and novel features of the invention will be set forth in the description which follows, and will become apparent to those skilled in the art upon examination of the following more detailed description and drawings in which like elements of the invention are similarly numbered throughout.